The world's largest biotechnology firm Amgen is buying US's cancer drug manufacturer Onyx Pharmaceuticals for about $10.4bn (£6.68bn, €7.68bn), offering $125 per share.

Onyx had spurned an earlier bid of $120 a share by Amgen and had assigned Centerview Partners the task of finding a suitable bidder.

Pfizer and Novartis were also reportedly interested in taking over Onyx but analysts had picked Amgen as the front-runner.

The deal, the largest for Amgen after it acquired Biotech firm Immunex in 2001 for $16bn, would give the company a strong presence in the $47.7bn cancer treatment market as it gains full rights to the drugs made by Onyx.

Cancer drugs are said to be the fastest growing segment in the pharmaceutical market. Onyx's cancer drug brand Kyproils is said to be notching up annual sales in excess of $2bn. Kyprolis, patented until 2025, has a good presence in the US.

With the deal, Amgen expects to have late-stage testing data of three experimental drugs for skin cancer, recurrent ovarian cancer and a medicine for bad cholesterol.

Amgen, with annual sales of $17.3bn, will also have access to Onyx and Pfizer's joint study on palbiciclib, a drug for breast cancer.

The deal which has been unanimously approved by the board of directors of both the companies is expected to be sealed by the beginning of the fourth quarter. It will be the biggest under the current CEO Robert A Bradway, who has to his credit a number of smaller deals.

"Amgen has a unique opportunity to add value to Kyprolis, a product which is at an early and promising stage of its launch," Bradway, said in a statement.

Lazard acted as the lead financial adviser for Amgen along with Bank of America Merrill Lynch which acted as a co-adviser and chief arranger of the finances for the company.

Hectic M&A Activity

The Amgen-Onyx deal adds to the ongoing hectic mergers and acquisitions activity in the healthcare sector. Last month, US-based pharmaceutical company Perrigo acquired Irish drugmaker Elan in a $8.6bn deal.

According to a Mergermaket report, there were 101 deals worth $6.6bn in the pharmaceutical, medical and biotech sectors during the first half of 2013 with the April to June quarter witnessing the highest number of deals.